public class Test1 {

    public static void main(String[] args) {
        String str = null;

        String temp = String.valueOf('a');
        str += temp;

        System.out.println(str);
    }

    public static void main1(String[] args) {
//        StringBuilder str = new StringBuilder();

//        String str = .toUpperCase('a');
        char ch = 'a';

//        str.append()
    }
}
